How do I get 100 backpack slots in Borderlands?

I was recently watching youtube videos trying to figure out how to kill Crawmerax the Invincible in Borderlands, as I mentioned in another thread. The guy doing the video had 100 slots in his backpack and he had absolutely tons of Pearlescent weapons. How did he get so many slots? And where did he get all the amazing wespons?! Do you just have to keep playing and playing to get all the good stuff?